Method and apparatus for fuel gas moisturization and heating

Abstract

Fuel gas is saturated with water heated with a heat recovery steam generator heat source. The heat source is preferably a water heating section downstream of the lower pressure evaporator to provide better temperature matching between the hot and cold heat exchange streams in that portion of the heat recovery steam generator. The increased gas mass flow due to the addition of moisture results in increased power output from the gas and steam turbines. Fuel gas saturation is followed by superheating the fuel, preferably with bottom cycle heat sources, resulting in a larger thermal efficiency gain compared to current fuel heating methods. There is a gain in power output compared to no fuel heating, even when heating the fuel to above the LP steam temperature.

What is claimed is:  
     
       1. A combined cycle system including a gas turbine, a steam turbine, and a heat recovery steam generator, wherein gas turbine exhaust gas is used in the heat recovery steam generator for generating steam for the steam turbine, said gas turbine exhaust gas flowing from an entry end to an exit end of the heat recovery steam generator, and wherein the system further comprises: 
       a fuel gas saturator having an inlet for hot saturator water, an inlet for fuel gas, an outlet for saturated fuel gas, and a saturator water outlet;  
       a saturator water heater;  
       a flow path for flowing saturator water from said saturator water outlet to said saturator heater, said saturator heater being operatively coupled to a heat source in the heat recovery steam generator for heating saturator water conducted thereto, using said heat source, to produce hot saturator water;  
       a flow path for flowing hot saturator water produced by the saturator heater to the hot saturator water inlet of the fuel gas saturator;  
       a fuel superheater for heating said saturated fuel gas;  
       a flow path for flowing saturated fuel gas from said saturated fuel gas outlet to said fuel superheater for heating said saturated fuel gas, to produce superheated, saturated fuel gas; and  
       a flow path for flowing said superheated, saturated fuel gas to said gas turbine.  
     
     
       2. A combined cycle system according to  claim 1 , wherein said fuel superheater is operatively coupled to a heat source in the heat recovery steam generator, for heating said saturated fuel gas using said heat source. 
     
     
       3. A combined cycle system according to  claim 2 , wherein said saturator heater is operatively coupled to a first portion of the heat recovery steam generator, said fuel superheater is operatively coupled to a second portion of the heat recovery steam generator, and wherein said second portion is upstream of said first portion with respect to a flow direction of said gas turbine exhaust through the heat recovery steam generator. 
     
     
       4. A combined cycle system according to  claim 1 , wherein said heat recovery steam generator includes a low pressure evaporator and wherein said heat source is downstream of said low pressure evaporator with respect to a flow direction of said gas turbine exhaust through the heat recovery steam generator. 
     
     
       5. A combined cycle system according to  claim 3 , wherein said heat recovery steam generator includes a low pressure evaporator, said first portion of the heat recovery steam generator is downstream of said low pressure evaporator with respect to a flow direction of said gas turbine exhaust through the heat recovery steam generator, and said second portion of the heat recovery steam generator is upstream of said low pressure evaporator. 
     
     
       6. A combined cycle system according to  claim 1 , further comprising an input for adding make up water from a make up water source to said saturator water for replacing moisture absorbed by the fuel gas. 
     
     
       7. A combined cycle system according to  claim 6 , wherein said input for adding make up water comprises a make up water inlet in said fuel gas saturator. 
     
     
       8. A combined cycle system according to  claim 6 , wherein said heat recovery steam generator includes at least one feed water transfer pump for pumping feed water therethrough, and said input for adding make up water includes a flow path for directing at least a portion of a feed water output from said feed water transfer pump to said fuel gas saturator. 
     
     
       9. A combined cycle system according to  claim 1 , wherein at least a portion of the water heated by the saturator heater is diverted to the fuel superheater for heating the saturated fuel. 
     
     
       10. A combined cycle system according to  claim 9 , wherein the heat source for said saturator heater is a different heat source than the heat source for said fuel superheater. 
     
     
       11. A combined cycle system according to  claim 1 , wherein said saturator heater comprises a heat exchanger for heating said saturator water with heat from said gas turbine exhaust, said heat exchanger being disposed in parallel to a low pressure economizer structure in said heat recovery steam generator. 
     
     
       12. A reheat cycle configuration for a steam turbine and gas turbine combined cycle system comprising: 
       a steam turbine connected to a load,  
       a condenser for receiving exhaust steam from the steam turbine and condensing said exhaust steam to water;  
       a heat recovery steam generator for receiving water from said condenser and converting said water to steam for return to said steam turbine;  
       at least one gas turbine for supplying heat to said heat recovery steam generator in the form of exhaust gases;  
       a fuel gas saturator assembly for saturating fuel gas with water and heating said fuel gas;  
       said heat recovery steam generator including a first water heater for heating water with heat from said exhaust gases, to define a heat source for water for said fuel gas saturator assembly; and  
       a fuel gas superheater for superheating fuel gas that has been saturated and heated by said fuel gas saturator assembly for supply to said gas turbine.  
     
     
       13. A reheat cycle configuration according to  claim 12 , wherein said a fuel gas saturator assembly comprises a water inlet for adding water to a fuel gas supply for said gas turbine and a heat exchanger for heating fuel gas saturated with water input at said water inlet; said heat exchanger receiving heated water from said first water heater. 
     
     
       14. A reheat cycle configuration according to  claim 12 , wherein said fuel gas saturator assembly comprises a fuel gas saturator packed column having an inlet for hot water from said first water heater, an inlet for fuel gas, an outlet for saturated fuel gas, and a water outlet. 
     
     
       15. A reheat cycle configuration according to  claim 12 , wherein said fuel gas superheater heats said saturated fuel gas with heat derived from said heat recovery steam generator. 
     
     
       16. A reheat cycle configuration according to  claim 12 , wherein at least a portion of the water heated by the first water heater is diverted to the fuel superheater for superheating the saturated fuel and wherein saturator water output from said fuel superheater is used to heat said fuel gas in said fuel gas saturator assembly. 
     
     
       17. A reheat cycle configuration according to  claim 16 , wherein said heat recovery steam generator includes a second water heater for heating said water diverted from said first water heater for input to said fuel superheater. 
     
     
       18. A reheat cycle configuration according to  claim 12 , wherein said first water heater is disposed in parallel to a low pressure economizer structure in said heat recovery steam generator. 
     
     
       19. A method for increasing power output and thermodynamic efficiency in a combined cycle system including a gas turbine, a steam turbine, and a heat recovery steam generator, wherein gas turbine exhaust gas is used in the heat recovery steam generator for generating steam for the steam turbine, said gas turbine exhaust gas flowing from an entry end to an exit end of the heat recovery steam generator, the method comprising the steps of: 
       adding water to and heating fuel gas to produce heated, saturated fuel gas, said fuel gas being heated with water heated by the heat recovery steam generator;  
       feeding the saturated fuel gas to a fuel superheater;  
       further heating the saturated fuel gas in the fuel superheater to superheat the fuel gas; and  
       feeding the superheated, saturated fuel gas to the gas turbine.  
     
     
       20. A method as in  claim 19 , wherein said saturated fuel gas is superheated with heat derived from a heat source in the heat recovery steam generator. 
     
     
       21. A method as in  claim 19 , wherein said fuel gas is saturated and heated in a fuel gas saturator packed column having an inlet for hot saturator water heated by the heat recovery steam generator, an inlet for fuel gas, an outlet for heated, saturated fuel gas, and a water outlet. 
     
     
       22. A method as in  claim 21 , wherein at least a portion of said hot saturator water is diverted to said fuel superheater before being fed to said saturator. 
     
     
       23. A method as in  claim 21 , wherein the saturator water is heated in a heat exchanger disposed downstream of a low pressure evaporator with respect to a flow direction of said gas turbine exhaust through the heat recovery steam generator. 
     
     
       24. A reheat cycle configuration according to  claim 12 , wherein said heat recovery steam generator includes low pressure evaporator, and wherein said first water heater comprises a heat exchanger disposed downstream of said low pressure evaporator with respect to a flow direction of said gas turbine exhaust through the heat recovery steam generator.